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Title:Manipulating lipid mesostructure using hard and soft material additives
Author(s):Steer, Dylan J
Director of Research:Leal, Cecilia
Doctoral Committee Chair(s):Leal, Cecilia
Doctoral Committee Member(s):Diao, Ying; Schweizer, Kenneth; Shim, Moonsub
Department / Program:Materials Science & Engineerng
Discipline:Materials Science & Engr
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Small-angle x-ray scattering
x-ray diffraction
self assembly
heirarchical structure
liquid crystal
lung surfactant
pulmonary surfactant
Abstract:Lipids are biological amphiphilic molecules that at their most basic level form a simple but important structural framework for cells. Lipids have recently increasingly been viewed as complex and active components of biological systems, but the majority of research continues to focus on biological aspects of their interactions within the plasma membrane. This is of course important but misses their great potential as self-assembled materials with complex structures at the nm length scale. In this dissertation, I explore in a largely abiological fashion how new materials can be created from some of the most well-studied lipids. My approach to this, and how the dissertation is roughly organized, is representative of two opposing approaches to complexity used in materials science. In a deconstructing approach, the focus is on reducing the system by identifying how or which components work together. This is useful when starting with a biological system with a built-in complexity. In a developmental approach, the focus is on merging relatively simple components to achieve cooperative or complementary behaviour. This takes engineered systems where we don't know the system's limits and work to expand the boundary. I characterize multilamellar assemblies of phospholipids with the intent of understanding the possible structural roles of the major lipid components present in healthy and diseased lungs. Mammalian breath relies on large periodic changes in the lung surface area. Lipids are naturally present to reduce the energy required for this motion, however, the efficacy depends on maintaining a healthy composition. Small-angle x-ray scattering (SAXS) is used to probe simple models of lung surfactant with up to 5 components. Supporting evidence of the hierarchical structure of lipid mixtures is collected using wide-angle x-ray scattering, solid-state NMR, and confocal fluorescence microscopy of multilamellar vesicles. I demonstrate first that the mitochondrial lipid cardiolipin, which is associated with symptoms of pneumonia, in high-humidity conditions both increases the membrane disorder and decreases the lipid mobility at physiological concentrations. A broader investigation demonstrates that cardiolipin causes adjacent bilayers to connect and fuse across the interlamellar space. Separately, I observe for the first time the formation of periodic asymmetrically phase-separated membranes in a simple 3-component mixture: a saturated lipid zwitterionic lipid DPPC, an unsaturated anionic lipid DOPG, and cholesterol. Lipid mixtures are well-known to phase separate spontaneously but are tightly coupled across the bilayer. Asymmetric phase separation usually requires either an active process as seen in vivo or careful sample preparation to control the composition of each half of the bilayer. Because asymmetric phase separation is important for studying the plasma membrane but difficult to prepare artificially, this result will help develop future models for the plasma membrane. Inorganic nanomaterials are structured at length scales where their size, shape, and organization determine their fundamental material properties. The most effective use of these materials can depend on controlling their relative separation and orientation at the individual particle or nm length scale over macroscopic distances. Bilayer-forming lipids are known to interact favourably with hydrophobic nanospheres and incorporate them up to around 5 nm total particle diameter. Most experimental evidence finds that larger particles are excluded. Here I demonstrate that GMO:DOTAP, a lipid mixture typically studied in the context of drug delivery, forms a composite structure with fluorescent CdSe/CdS dot-in-rod that neither structure can form independently. Using glancing incidence SAXS I demonstrate that low-aspect-ratio nanorods co-assemble with lipids into a non-close-packed liquid crystalline phase with square-shaped symmetry. This is one of very few experimental systems that can induce rod-shaped particles to form a square lattice. I further discover that the assembly is kinetically controlled and that when dried quickly, the nanorod-composites self-assemble into a currently unidentified 3D structure. The new assembly can be oriented relative to a substrate using both drop-casting and spin-coating techniques. The lattice parameter of the structure and therefore the nanorod separation can be reversibly controlled using the relative humidity surrounding the films at length scales of a few nm. Because interactions between nanomaterials are determined over these distances, this structure is promising for future applications in responsive functional devices.
Issue Date:2021-03-09
Rights Information:Copyright 2021 Dylan Steer
Date Available in IDEALS:2021-09-17
Date Deposited:2021-05

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